Exploring the toppling deformation mechanisms and failure modes of anti-dip layered rocky slopes: insights from physical model experiments

In the southwestern mountainous regions of China, slope toppling failures are prevalent in engineering construction and disaster mitigation, influenced by critical geological parameters such as slope height, slope angle, bedding angle, lithology, and fracture depth. To elucidate the deformation mechanisms of toppling in anti-dip slopes, limestone and shale from the Guang'an Village landslide were used as prototypes to create similar materials for physical model experiments on anti-dip layered limestone slopes (ALL) and shale slopes (ALS). These experiments simulated gravitational effects over geological timescales by applying loads at the slope top and utilized digital photography, non-contact deformation measurement technology, and miniature pressure sensors to capture real-time imagery, displacement, and pressure data. The results successfully replicated the entire toppling process within anti-dip rocky slopes, revealing distinct deformation mechanisms and failure modes across different lithologies. Hard rock layers like limestone showed susceptibility to brittle failure, characterized by toppling and fracturing, while soft rock layers like shale were prone to long-term bending creep. The study observed distinct toppling behaviors leading to different failure modes; the ALL slope exhibited shallow collapses, while the ALS slope was more susceptible to deep-seated sliding events. A novel grading system integrating qualitative and quantitative indicators was proposed, using the overturning angle of rock layers as a key parameter for describing kinematic characteristics and facilitating a phased analysis of the toppling processes in both stable and unstable regions. In ALL slope, horizontal displacement vectors predominated, highlighting rotational deformation around the slope toe after the rock layers experiencing toppling fracture. Conversely, ALS slope demonstrated a gradual increase in vertical displacement from the surface inward, indicative of a bending toppling mode. Notably, during load application, internal pressures within the rock mass at the slope surface and the front edge of the slope top exhibited marked, stepwise significant changes, underscoring a dynamic shift between tensile and compressive stresses. This study provides essential data for geological engineering stability assessments, risk prediction, and design, serving as a valuable case study for exploring the deformation and failure mechanisms of anti-dip layered rocky slopes.